JP3780859B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device that allows an exhaust gas to be switched and passed alternately from an exhaust upstream side and a downstream side to a filter of the purification device.
[0002]
[Prior art]
Conventionally, in a diesel engine, in order to remove particulates such as soot contained in exhaust gas, a particulate filter is arranged in the engine exhaust passage, and particulates in the exhaust gas are once collected by this particulate filter, The particulate filter is regenerated by causing the particulates collected on the particulate filter to ignite and burn. However, the fine particles collected on the particulate filter are not ignited unless the temperature is about 600 ° C. or higher. On the other hand, the exhaust gas temperature of a diesel engine is usually much lower than 600 ° C. Therefore, it is difficult to ignite the particulates collected on the particulate filter with the exhaust gas heat, and the particulates have a low temperature to ignite the particulates collected on the particulate filter with the exhaust gas heat. It must be possible to ignite with.
[0003]
By the way, it has been conventionally known that if the catalyst is supported on the particulate filter, the ignition temperature of the fine particles can be lowered. Therefore, conventionally, various particulate filters supporting the catalyst are used to lower the ignition temperature of the fine particles. It is known.
[0004]
For example, Japanese Patent Publication No. 7-106290 discloses a particulate filter in which a mixture of a platinum group metal and an alkaline earth metal oxide is supported on a particulate filter. In this particulate filter, fine particles are ignited at a relatively low temperature of about 350 ° C. to 400 ° C., and then burned continuously.
[0005]
[Problems to be solved by the invention]
In a diesel engine, if the load increases, the exhaust gas temperature reaches 350 ° C. to 400 ° C. Therefore, at first glance, the above particulate filter can ignite and burn particulates by the exhaust gas heat when the engine load increases. looks like. In practice, however, the particulate matter may not ignite even when the exhaust gas temperature reaches 350 ° C. to 400 ° C. Even if the particulate matter ignites, only a part of the particulate matter burns, and a large amount of particulate matter remains unburned. Is produced.
[0006]
That is, when the amount of fine particles contained in the exhaust gas is small, the amount of fine particles adhering to the particulate filter is small. At this time, when the exhaust gas temperature is 350 ° C. to 400 ° C., the fine particles on the particulate filter are ignited and then continuously Can be burned.
[0007]
However, when the amount of particulates contained in the exhaust gas increases, other particulates accumulate on the particulates before the particulates adhering to the particulate filter completely burn, and as a result, the particulates are stacked on the particulate filter. It accumulates in the shape. When fine particles are deposited in a layered manner on the particulate filter in this way, some of the fine particles that easily come into contact with oxygen are burned, but the remaining fine particles that are difficult to come into contact with oxygen do not burn, and thus a large amount of fine particles are not burned. It will remain unburned. Therefore, when the amount of fine particles contained in the exhaust gas increases, a large amount of fine particles continue to accumulate on the particulate filter.
[0008]
On the other hand, when a large amount of fine particles are deposited on the particulate filter, the deposited fine particles gradually become difficult to ignite and burn. The reason why it becomes difficult to burn in this way is probably because the carbon in the fine particles changes to graphite or the like which is difficult to burn during the deposition. In fact, if a large amount of fine particles continue to be deposited on the particulate filter, the deposited fine particles are not ignited at a low temperature of 350 ° C. to 400 ° C., and a high temperature of 600 ° C. or higher is required to ignite the deposited fine particles. However, in a diesel engine, the exhaust gas temperature usually does not reach a high temperature of 600 ° C. or higher. Therefore, if a large amount of particulates continues to accumulate on the particulate filter, it becomes difficult to ignite the particulates deposited by the exhaust gas heat.
[0009]
Further, when the deposited fine particles are burned, the ash that is burned residue, that is, the ash condenses into large lumps, and these ash lumps clog the pores of the particulate filter. The number of clogged pores gradually increases with time, and thus the pressure loss of the exhaust gas flow in the particulate filter gradually increases. When the pressure loss of the exhaust gas flow increases, the output of the engine decreases, and thus the problem arises that the particulate filter must be replaced with a new one at this point.
[0010]
Once such a large amount of fine particles accumulates in the form of a laminate, various problems as described above arise, and therefore the balance between the amount of fine particles contained in the exhaust gas and the amount of fine particles that can burn on the particulate filter is considered. Therefore, it is necessary to prevent a large amount of fine particles from being deposited on the laminate.
[0011]
Then, if the exhaust purification is a continuous combustion process that is dependent on the operating state of the internal combustion engine by simply providing a conventional exhaust purification filter with a catalyst in the exhaust pipe, the above problems cannot be avoided.
[0012]
Therefore, the particulate matter accumulates on both sides of the filter by allowing the exhaust gas to alternately switch from the upstream side and the downstream side of the exhaust gas so that the continuous combustion of the particulate matter is possible. In addition, the amount of fine particles deposited per unit area can be reduced, and the fine particles deposited can be disturbed by switching the exhaust gas flow. Furthermore, if a NOx absorbent is provided on the filter base material, NOx in the exhaust gas can be purified.
[0013]
As described above, when a NOx absorbent is provided on the filter base material for simultaneously purifying NOx, the NOx absorbent capacity of the NOx absorbent is limited, so that a rich air-fuel ratio exhaust gas is allowed to flow intermittently through the filter. It is necessary to release and reduce NOx from the NOx absorbent (this is called rich spike). On the other hand, in order to switch the direction of the exhaust gas flowing through the filter as described above in order to promote the continuous combustion of fine particles, it is necessary to provide a switching valve in the exhaust pipe, but due to the structure of the switching valve, when switching the exhaust gas flow It is inevitable that the exhaust gas flows around the filter.
[0014]
Therefore, when the execution timing of the rich spike coincides with the switching timing of the exhaust gas flow by the switching valve, the rich air-fuel ratio exhaust gas containing a large amount of reducing agent may be released without passing through the filter.
[0015]
Further, in the exhaust purification filter in which the NOx absorbent is provided on the filter base material in order to simultaneously remove particulates and purify NOx, when the particulate oxidation performance in the filter is not sufficient, or the temperature of the exhaust gas is low, When there is a possibility of reducing the oxidation performance of the particulates (for example, during deceleration operation), in order to prevent more than a set amount of particulates from accumulating on the filter, a system that bypasses the filter and flows exhaust gas is used. It is possible.
[0016]
Even when such a system is used, when the rich spike for NOx purification is executed while exhaust gas is flowing around the filter, the rich air-fuel ratio exhaust gas containing a large amount of reducing agent is also produced. It will be discharged without passing through the filter.
[0017]
The present invention has been made in view of the above points. In an exhaust gas purification apparatus equipped with a filter with an NOx absorbent, an exhaust gas containing a large amount of a reducing agent necessary for releasing NOx from the NOx absorbent is not present. It is an object to prevent the product from being released as it is processed.
[0018]
Further, according to the present invention, when unburned fuel is supplied to the filter in order to improve the particulate oxidation removal capability by the filter, the unburned fuel is bypassed through the filter and discharged outside the vehicle without being supplied to the filter. It is an object of the present invention to provide an exhaust gas purification apparatus for an internal combustion engine that can avoid this.
[0019]
Furthermore, according to the present invention, when exhaust gas having a relatively small exhaust gas air-fuel ratio including HC, CO, unburned fuel, etc. is flowing, the exhaust gas is discharged into the atmosphere without passing through the particulate filter. It is an object of the present invention to provide an exhaust gas purification apparatus for an internal combustion engine that can avoid this.
[0023]
[Means for Solving the Problems]
  In order to solve the above-described problems, in the first invention, (a) a filter that collects particulates in exhaust gas for a period of time and oxidizes and removes (b) a first flow of exhaust gas from one side of the filter. A flow and a second flow through which the exhaust gas flows from the other side of the filter can be switched alternately, and during the switching, exhaust switching means for the exhaust gas to flow around the filter; Unburned fuel supply means for supplying the fuel, (d) execution of unburned fuel supply by the unburned fuel supply means and switching operation of the exhaust gas flow by the exhaust gas switching means are performed simultaneously. A simultaneous processing prohibiting means for prohibitingIn an exhaust gas purification apparatus for an internal combustion engine, the filter has a plurality of exhaust flow passages defined by partition walls formed of a porous material, and the exhaust gas flow into the filter passes through the partition walls. Thus, the exhaust flow passage is closed at the upstream end or downstream end, and the wall surfaces of the partition walls of the filter are utilized by alternately switching the first flow and the second flow by the exhaust gas switching means. To collect and oxidize and remove particulates in the exhaust gas.
[0024]
  According to thisBy supplying unburned fuel to the filter, the unburned fuel is also oxidized in the filter and the filter temperature rises. At this time, by switching the flow of the exhaust gas, the heat of oxidation cannot flow out of the filter, and the filter temperature is further increased. By this temperature rise of the filter, the ability of the filter to oxidize and remove fine particles can be improved. Therefore, it can be said that it is preferable to supply unburned fuel to the filter at a predetermined time. On the other hand, if the supply of unburned fuel and the operation of the exhaust gas switching means are performed simultaneously, the unburned fuel is It bypasses the filter and is discharged outside the vehicle. Therefore, by providing a simultaneous processing prohibiting means for preventing the supply of unburned fuel and the operation of the exhaust gas switching means from being performed simultaneously, the unburned fuel is supplied to the filter when the unburned fuel is supplied to the filter. It is possible to avoid being discharged outside the vehicle by bypassing the filter without being supplied.
[0025]
  Also,In the second invention(B) NOx absorbent that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases, and active oxygen that promotes oxidation of fine particles (B) The air-fuel ratio of the exhaust gas flowing through the filter in order to release NOx from the NOx absorbent carried on the filter. Exhaust air / fuel ratio control means for controlling the air / fuel ratio or rich air / fuel ratio, and (c) The exhaust gas is normally allowed to flow through the filter, and the particulate oxidation performance in the filter may be lower or lower than a predetermined level. And (d) exhaust gas air-fuel ratio control is executed by the exhaust air-fuel ratio control means to bypass the filter when the exhaust gas flows. When NOx is released from the NOx absorbent carried on the filter, the exhaust gas switching means bypasses the filter and allows the exhaust gas to flow even if the oxidation performance of the particulates in the filter is lower than the predetermined level. And a detour prohibition means to prohibitThe
[0026]
  According to thisIn principle, when the oxidation performance of the particulates in the filter is lower than the predetermined level, the exhaust gas switching means causes the exhaust gas to flow around the filter, so that particulates exceeding the set value are deposited on the filter. Is prevented. However, when NOx is released from the NOx absorbent, even if the particulate oxidation performance in the filter is lower than the predetermined level, the bypass prohibiting means causes the exhaust gas to flow around the filter. The exhaust gas controlled to the theoretical air-fuel ratio or rich air-fuel ratio to release NOx from the NOx absorbent is discharged untreated without passing through the filter. There is nothing to do.
[0027]
  Also,First2The exhaust gas switching means in the invention is usually exhaust gasTheIt is sufficient if it has a function of flowing exhaust gas by bypassing the filter when the particulate oxidation performance in the filter is lower than a predetermined level or when there is a possibility that it will become lower.TheFirst flow of exhaust gas from one side of the filterAnd fuThe function of alternately switching the second flow of flowing the exhaust gas from the other side of the filter is not necessarily required, but such a function may be provided.
[0028]
  Also,First2In the invention ofTheThe case where the oxidation performance in the filter is lower than a predetermined level can be, for example, during engine load reduction operation (in the case of a vehicle drive internal combustion engine, during vehicle deceleration operation).
  The above configurations can be combined with each other as much as possible.
[0029]
  Also,In the third inventionA particulate filter for collecting particulates in the exhaust gas discharged from the combustion chamber is disposed in the engine exhaust passage, and particulates in the exhaust gas are captured when the exhaust gas passes through the walls of the particulate filter. In the exhaust gas purification apparatus for an internal combustion engine, the particulate filter is capable of oxidizing particulates temporarily collected by the particulate filter, and the exhaust gas that passes through the wall of the particulate filter. Exhaust gas backflow means for reversing the gas flow is provided, and the exhaust gas backflow means has a bypass mode in which the exhaust gas bypasses the particulate filter without flowing into the particulate filter, When the first exhaust gas having a relatively small gas air-fuel ratio is flowing, the exhaust gas Prohibits the flow means is arranged in the bypass mode, allowing the said exhaust gas backflow means are arranged in the bypass mode when a relatively large second exhaust gas in the exhaust gas air-fuel ratio is flowingThe
[0030]
  Also,In the fourth inventionThe second3DepartureClearlyIn this case, when the first exhaust gas having a relatively small exhaust gas air-fuel ratio is flowing, the exhaust gas that passes through the wall of the particulate filter in order to avoid the exhaust gas backflow means being placed in the bypass mode. When reversing the gas flow is prohibited and the second exhaust gas having a relatively large exhaust gas air-fuel ratio is flowing, the exhaust gas flow is reversed as the exhaust gas flow passing through the wall of the particulate filter is reversed. Allow gas backflow means to be placed in bypass modeThe
[0031]
  Also,In the fifth inventionThe second3DepartureClearlyIn this case, when it is necessary to reverse the flow of the exhaust gas passing through the wall of the particulate filter while the first exhaust gas having a relatively small exhaust gas air-fuel ratio is flowing, The exhaust gas air-fuel ratio is increased while prohibiting reversal of the flow of exhaust gas passing through the wall of the particulate filter, and then reversal of the flow of exhaust gas passing through the wall of the particulate filter is allowed.The
[0032]
  Also,In the sixth inventionThe second3DepartureClearlyThe first exhaust gas having a relatively small exhaust gas air-fuel ratio is stoichiometric or rich, and the second exhaust gas having a relatively large exhaust gas air-fuel ratio is lean.The
[0033]
  First3To the second6InventionAccording toWhen the first exhaust gas having a relatively small exhaust gas air-fuel ratio is flowing, ExhaustIt is prohibited to place the gas backflow means in bypass mode.And thereforeThe exhaust gas is prohibited from bypassing the particulate filter without flowing into the particulate filter. Therefore, exhaust gas containing HC, CO, unburned fuel, etc. with a relatively small exhaust gas air-fuel ratioIsBypassing without passing through the particulate filter, it is possible to avoid being discharged into the atmosphere.
[0034]
  Also,In the seventh inventionThe second3DepartureClearlyThe NOx absorbent that absorbs NOx in lean and releases NOx in stoichiometric or rich form is supported on the particulate filter, and when the NOx should be released from the NOx absorbent, the exhaust gas air-fuel ratio is made relatively small, When the NOx absorbent is releasing NOx, it is prohibited to reverse the flow of the exhaust gas passing through the wall of the particulate filter in order to avoid the exhaust gas backflow means being placed in the bypass mode.The
[0035]
  According to thisWhen the exhaust gas air-fuel ratio is relatively small and the NOx absorbent is releasing NOx, the exhaust gas passing through the particulate filter wall to avoid the exhaust gas backflow means being placed in the bypass mode. Reversal of gas flow is prohibited. Therefore, to release NOx from the NOx absorbentHExhaust gas with relatively small exhaust gas air-fuel ratio, including C, CO, unburned fuel, etc.IsBypassing without passing through the particulate filter, it is possible to avoid being discharged into the atmosphere.
[0036]
  Also,In the eighth inventionThe second3DepartureClearlyHowever, as the amount of inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, further increasing the amount of inert gas supplied to the combustion chamber. As a result, an internal combustion engine in which the temperature of the fuel during combustion in the combustion chamber and the surrounding gas temperature is lower than the generation temperature of soot so that soot is hardly generated, and the fuel during combustion in the combustion chamber and the surroundings When the exhaust gas discharged from the combustion chamber is flowing during low temperature combustion where the gas temperature is lower than the soot generation temperature and soot is hardly generated, the exhaust gas backflow means is placed in the bypass mode. BanThe
[0037]
  According to this, lowWhen exhaust gas discharged from the combustion chamber is flowing during warm combustion, it is prohibited to place the exhaust gas backflow means in the bypass mode. for that reasonLowExhaust gas exhausted from the combustion chamber during hot combustion and having a relatively small exhaust gas air-fuel ratio including HC, CO, unburned fuel, etc.IsBypassing without passing through the particulate filter, it is possible to avoid being discharged into the atmosphere.
[0038]
  Also,In the ninth inventionThe second8DepartureClearlyDuring the SOx poisoning recovery, NOx release, or engine low load operation, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is lower than the generation temperature of soot, and soot is generated. When exhaust gas discharged from the combustion chamber is flowing during low-temperature combustion that hardly occurs, the exhaust gas backflow means is prohibited from being placed in the bypass mode.The
[0039]
  According to this, During SOx poisoning recovery, NOx release, or engine low load operationLowWhen exhaust gas discharged from the combustion chamber is flowing during warm combustion, it is prohibited to place the exhaust gas backflow means in the bypass mode. Therefore, at the time of SOx poisoning recovery, NOx release, or engine low load operation,LowExhaust gas containing HC, CO, unburned fuel, etc. discharged from the combustion chamber during warm combustionIsBypassing without passing through the particulate filter, it is possible to avoid being discharged into the atmosphere.
[0040]
  Also,In the tenth inventionA particulate filter for collecting particulates in the exhaust gas discharged from the combustion chamber is disposed in the engine exhaust passage, and particulates in the exhaust gas are captured when the exhaust gas passes through the walls of the particulate filter. In the exhaust gas purification apparatus for an internal combustion engine, the particulate filter can oxidize particulates temporarily collected by the particulate filter, absorbs NOx with lean, and is stoichiometric or rich. An NOx absorbent for releasing NOx is carried on the particulate filter, and exhaust gas backflow means for reversing the flow of exhaust gas passing through the wall of the particulate filter is provided, and the exhaust gas backflow means includes exhaust gas Bypasses the particulate filter without flowing into the particulate filter. In the case where the exhaust gas backflow means should be placed in the bypass mode and NOx should be released from the NOx absorbent when the particulate filter's oxidation performance by the particulate filter is lower than a predetermined level. However, even if the particulate filter oxidation performance by the particulate filter is lower than the predetermined level, the exhaust gas backflow means is prohibited from being placed in the bypass mode.The
[0041]
  According to thisUsually, for example, when the particulate oxidation performance by the particulate filter is lower than a predetermined level, such as during engine deceleration operation, the exhaust gas backflow means is disposed in the bypass mode, and NOx should be released from the NOx absorbent. Even when the particulate oxidation performance by the particulate filter is lower than the predetermined level, the exhaust gas backflow means is prohibited from being placed in the bypass mode. For this reason, normally, when the particulate filter oxidation performance of the particulate filter is lower than a predetermined level, the amount of particulate accumulation in the particulate filter increases as exhaust gas that may contain particulates passes through the particulate filter. In the case where NOx should be released from the NOx absorbent while suppressing this, exhaust gas containing HC, CO, unburned fuel, etc. bypasses the particulate filter in order to release NOx from the NOx absorbent. It is possible to prevent the exhaust gas from being discharged into the atmosphere as it is.
[0042]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described below with reference to the drawings of FIGS.
[First Embodiment]
First, a first embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings of FIGS.
[0043]
<Outline of device configuration>
FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine for a vehicle. The present invention can also be applied to a spark ignition type internal combustion engine.
Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Is an exhaust valve, and 10 is an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a compressor 15 of an exhaust turbocharger 14 via an intake duct 13. A throttle valve 17 driven by a step motor 16 is disposed in the intake duct 13, and a cooling device 18 for cooling intake air flowing through the intake duct 13 is disposed around the intake duct 13. In the embodiment shown in FIG. 1, engine cooling water is guided in the cooling device 18, and the intake air is cooled by the engine cooling water. On the other hand, the exhaust port 10 is connected to an exhaust turbine 21 of an exhaust turbocharger 14 via an exhaust manifold 19 and an exhaust pipe 20, and an outlet of the exhaust turbine 21 is connected to an exhaust purification device having a casing 23 containing a particulate filter 22. Is done.
[0044]
The exhaust manifold 19 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 24, and an electrically controlled EGR control valve 25 is disposed in the EGR passage 24. A cooling device 26 for cooling the EGR gas flowing in the EGR passage 24 is disposed around the EGR passage 24. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 26, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, so-called common rail 27, through a fuel supply pipe 6a. Fuel is supplied into the common rail 27 from an electrically controlled fuel pump 28 with variable discharge amount, and the fuel supplied into the common rail 27 is supplied to the fuel injection valve 6 via each fuel supply pipe 6a. A fuel pressure sensor 29 for detecting the fuel pressure in the common rail 27 is attached to the common rail 27, and a fuel pump 28 is set so that the fuel pressure in the common rail 27 becomes a target fuel pressure based on an output signal of the fuel pressure sensor 29. The discharge amount is controlled.
[0045]
The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, an input port 35 and an output port 36 are connected. It comprises. The output signal of the fuel pressure sensor 29 is input to the input port 35 via the corresponding AD converter 37. A temperature sensor 39 for detecting the temperature of the particulate filter 22 is attached to the particulate filter 22, and an output signal of the temperature sensor 39 is input to the input port 35 via the corresponding AD converter 37. . A load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. . Further, a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 30 ° is connected to the input port 35. On the other hand, the output port 36 is connected to the fuel injection valve 6, the throttle valve driving step motor 16, the EGR control valve 25, the fuel pump 28, and an actuator 72 described later via a corresponding drive circuit 38.
[0046]
FIG. 2A shows the relationship between the required torque TQ, the amount of depression L of the accelerator pedal 40, and the engine speed N. In FIG. 2A, each curve represents an equal torque curve, a curve indicated by TQ = 0 indicates that the torque is zero, and the remaining curves are TQ = a, TQ = b, The required torque gradually increases in the order of TQ = c and TQ = d. The required torque TQ shown in FIG. 2 (A) is stored in advance in the ROM 32 in the form of a map as a function of the depression amount L of the accelerator pedal 40 and the engine speed N as shown in FIG. 2 (B). In the embodiment according to the present invention, the required torque TQ corresponding to the depression amount L of the accelerator pedal 40 and the engine speed N is first calculated from the map shown in FIG. 2B, and the fuel injection amount is calculated based on the required torque TQ. Etc. are calculated.
[0047]
<Structure of exhaust purification device>
In the exhaust emission control device, an exhaust pipe 70 is connected to the outlet of the exhaust turbine 21 as shown in FIGS. A first exhaust passage 76 and a second exhaust passage 77 branched from the exhaust pipe 70 and respectively connected to one surface and the other surface of the filter 22 in the casing 23 containing the particulate filter 22 are provided. Is provided. Further, a bypass passage 73 is provided for discharging exhaust gas as it is without passing through the particulate filter 22 from the branch point of the first exhaust passage 76 and the second exhaust passage 77.
[0048]
An exhaust switching valve 71 is provided at a branch point between the first exhaust passage 76 and the second exhaust passage 77. The exhaust switching valve 71 is driven by an actuator 72, selects a first exhaust passage 76, selects a first flow (forward flow) through which exhaust gas flows from one side of the filter 22, and selects a second exhaust passage 77. Then, the second flow (back flow) for flowing the exhaust gas from the other side of the filter 22 is alternately switched.
[0049]
Here, the casing 23 that accommodates the filter 22 is arranged to be positioned directly above the exhaust pipe 70 that forms the bypass passage 73, and a first exhaust passage 76 that branches from the exhaust pipe 70 on both sides of the casing 23. The second exhaust passage 77 is connected. The filter 22 in the casing 23 has a length in the width direction orthogonal to the length direction longer than the length in the length direction when the exhaust gas passage direction is the length direction. By setting it as such a structure, the mounting space to the vehicle of the exhaust gas purification apparatus which consists of the casing 23 which encloses the filter 22 can be saved.
[0050]
The actuator 72 is driven and controlled by the control means 75 realized on the CPU 34 of the electronic control unit 30, and is driven by a control signal from the output port 36. The actuator 72 is driven by a negative pressure formed as the internal combustion engine is driven, and the valve body is located at a position (forward flow position) where the first exhaust passage 76 is selected when no negative pressure is applied. When the first negative pressure is applied, the valve body is controlled to the neutral position, and when the second negative pressure stronger than the first negative pressure is applied, the second exhaust passage 77 is selected. The valve body is controlled to the position (backflow position).
[0051]
When the valve body is in the forward flow position indicated by the broken line in FIG. 3, the exhaust switching valve 71 connects the exhaust pipe 70 to the first exhaust passage 76 and connects the second exhaust passage 77 to the bypass passage 73. Therefore, the exhaust gas flows in the order of the exhaust pipe 70 → the first exhaust passage 76 → the filter 22 → the second exhaust passage 77 → the bypass passage 73 and is released to the atmosphere.
[0052]
When the valve body is in the backflow position indicated by the solid line in FIG. 3, the exhaust switching valve 71 connects the exhaust pipe 70 to the second exhaust passage 77 and connects the first exhaust passage 76 to the bypass passage 73. Therefore, the exhaust gas flows in the order of the exhaust pipe 70 → the second exhaust passage 77 → the filter 22 → the first exhaust passage 76 → the bypass passage 73 and is released to the atmosphere.
[0053]
When the valve body is in a neutral position parallel to the axis of the exhaust pipe 70 as shown by a one-dot chain line in FIG. 3, the exhaust switching valve 71 connects the exhaust pipe 70 directly to the bypass passage 73. The gas flows from the exhaust pipe 70 to the bypass passage 73 without passing through the filter 22 and is released to the atmosphere.
[0054]
By switching forward and backward flow by switching the valve body, fine particles such as soot move around in the base material of the filter 22, so that the oxidation of the fine particles is promoted, so that the fine particles can be purified efficiently.
[0055]
FIG. 5A is an image diagram when exhaust gas is allowed to flow through the filter 22 only from one direction. The particulates accumulate only on one surface of the filter and do not move, and only cause an increase in exhaust gas pressure loss. Without hindering the purification of particulates.
[0056]
FIG. 5B is an image diagram when exhaust gas is allowed to flow through the filter 22 from both directions. Since the fine particles are disturbed in the forward flow direction and the reverse flow direction on both sides of the filter, both sides of the filter 22 or the substrate It can move around and promote the oxidation of the fine particles by utilizing the active points of the entire filter substrate, and the accumulation of fine particles in the filter 22 can be reduced. Therefore, an increase in exhaust gas pressure loss can be avoided.
[0057]
<Filter structure>
FIG. 6 shows the structure of the particulate filter 22. 6A shows a front view of the particulate filter 22, and FIG. 6B shows a side sectional view of the particulate filter 22. As shown in FIG. As shown in FIGS. 6A and 6B, the particulate filter 22 has a honeycomb structure and is a so-called wall flow type having a plurality of exhaust flow passages 50 and 51 extending in parallel with each other. . These exhaust flow passages are configured by an exhaust gas circulation passage 50 whose downstream end is closed by a plug 52 and an exhaust gas outflow passage 51 whose upstream end is closed by a plug 53. In FIG. 6A, the hatched portion indicates the plug 53. Therefore, the exhaust gas inflow passages 50 and the exhaust gas outflow passages 51 are alternately arranged via the thin partition walls 54. In other words, the exhaust gas inflow passage 50 and the exhaust gas outflow passage 51 are each surrounded by the four exhaust gas outflow passages 51, and each exhaust gas outflow passage 51 is surrounded by the four exhaust gas inflow passages 50. Arranged so that.
[0058]
The particulate filter 22 is made of, for example, a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage 50 is contained in the surrounding partition wall 54 as indicated by an arrow in FIG. Through the exhaust gas outflow passage 51 adjacent thereto.
[0059]
In the embodiment according to the present invention, a carrier layer made of alumina, for example, is formed on the peripheral wall surfaces of the exhaust gas inflow passages 50 and the exhaust gas outflow passages 51, that is, on both side surfaces of the partition walls 54 and on the pore inner wall surfaces of the partition walls 54. The noble metal catalyst is formed on this support, and when there is excess oxygen in the surroundings, oxygen is taken in and retained, and when the surrounding oxygen concentration decreases, the active oxygen form releases the retained oxygen. An oxygen release agent and a NOx absorbent that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases are carried.
[0060]
Here, the air-fuel ratio of the exhaust gas flowing into the NOx absorbent means the ratio of air and fuel (hydrocarbon) supplied into the engine intake passage, the combustion chamber 5 and the exhaust passage upstream of the NOx absorbent. When fuel (hydrocarbon) or air is not supplied into the exhaust passage upstream of the NOx absorbent, the air-fuel ratio of the inflowing exhaust gas matches the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber.
[0061]
Platinum Pt can be used as the noble metal catalyst.
Examples of the active oxygen releasing agent include alkali metals such as potassium K, sodium Na, lithium Li, cesium Cs, and rubidium Rb, alkaline earth metals such as barium Ba, calcium Ca, and strontium Sr, lanthanum La, and yttrium Y. And at least one selected from rare earths and transition metals.
[0062]
In this case, as the active oxygen release agent, it is preferable to use an alkali metal or alkaline earth metal having a higher ionization tendency than calcium Ca, that is, potassium K, lithium Li, cesium Cs, rubidium Rb, barium Ba, and strontium Sr. .
[0063]
Examples of the NOx absorbent include alkali metals such as potassium K, sodium Na, lithium Li, cesium Cs, and rubidium Rb, alkaline earths such as barium Ba, calcium Ca, and strontium Sr, lanthanum La, and yttrium Y. It can be composed of at least one selected from rare earths.
[0064]
In this case, as the NOx absorbent, it is preferable to use an alkali metal or alkaline earth metal having a higher ionization tendency than calcium Ca, that is, potassium K, lithium Li, cesium Cs, rubidium Rb, barium Ba, and strontium Sr.
[0065]
As can be seen from a comparison between the metal constituting the active oxygen release agent and the metal constituting the NOx absorbent, the metals constituting these are largely the same.
Therefore, different metals can be used as the active oxygen release agent and the NOx absorbent, respectively, or the same metal can be used. When the same metal is used as the active oxygen release agent and the NOx absorbent, the metal functions simultaneously as both an active oxygen release agent and a NOx absorbent. Thus, what performs the function of both the function of an active oxygen releasing agent and the function of a NOx absorbent simultaneously is hereinafter referred to as “active oxygen releasing / NOx absorbent”.
[0066]
In this embodiment, a case where platinum Pt as a noble metal catalyst and potassium K as an active oxygen release / NOx absorbent are supported on a support such as alumina will be described as an example.
[0067]
As described above, potassium K as an active oxygen release / NOx absorbent simultaneously functions as both an active oxygen release agent and a NOx absorbent. The function as an oxygen releasing agent is used to promote the oxidation removal of fine particles in the exhaust gas, and the function as a NOx absorbent is used to purify NOx in the exhaust gas. Hereinafter, the purification mechanism in the exhaust gas purification apparatus will be described focusing on the respective functions.
[0068]
<Continuous Oxidation Treatment of Fine Particles with Filter ... Function as Active Oxygen Release Agent>
First, the action of removing particulates in the exhaust gas by the particulate filter 22 utilizing the function of the active oxygen release / NOx absorbent as the active oxygen release agent will be described. The function as the active oxygen release agent is such that the fine particle removing action is performed by the same mechanism even when other alkali metal, alkaline earth metal, rare earth, and transition metal are used as the active oxygen release agent.
[0069]
In a compression ignition type internal combustion engine as shown in FIG. 1, combustion is performed under an excess of air, and therefore the exhaust gas contains a large amount of excess air. That is, in the compression ignition type internal combustion engine as shown in FIG. 1, the air-fuel ratio of the exhaust gas is lean. Further, since NO is generated in the combustion chamber 5, the exhaust gas contains NO. The fuel also contains sulfur S, which reacts with oxygen in the combustion chamber 5 to react with SO.₂It becomes. Therefore, in the exhaust gas, SO₂It is included. Therefore excess oxygen, NO and SO₂The exhaust gas containing the gas flows into the exhaust gas inflow passage 50 of the particulate filter 22.
[0070]
7A and 7B schematically show enlarged views of the surface of the carrier layer formed on the inner peripheral surface of the exhaust gas inflow passage 50 and the inner wall surface of the fistula in the partition wall 54. FIG. 7A and 7B, reference numeral 60 denotes particles of platinum Pt, and reference numeral 61 denotes an active oxygen release / NOx absorbent containing potassium K.
[0071]
As described above, since the exhaust gas contains a large amount of excess oxygen, when the exhaust gas flows into the exhaust gas inflow passage 50 of the particulate filter 22, as shown in FIG.₂Is O₂ ^-Or O^2-The surface of platinum Pt adheres in the form of On the other hand, NO in the exhaust gas is O on the surface of platinum Pt.₂ ^-Or O^2-Reacts with NO₂(2NO + O₂→ 2NO₂). Then the generated NO₂Part of the oxygen is oxidized on platinum Pt while being absorbed into the active oxygen release / NOx absorbent 61 and combined with potassium K, as shown in FIG._Three ^-In the form of active oxygen release and NOx absorbent 61 diffused in the form of some nitrate ions NO_Three ^-Is potassium nitrate KNO_ThreeIs generated.
[0072]
On the other hand, as described above, the exhaust gas contains SO.₂Is also included, this SO₂Is absorbed into the active oxygen release / NOx absorbent 61 by the same mechanism as NO. That is, as described above, oxygen O₂Is O₂ ^-Or O₂ ^-Is attached to the surface of platinum Pt in the form of SO₂Is O on the surface of platinum Pt.₂ ^-Or O^2-Reacts with SO_ThreeIt becomes.
[0073]
The generated SO_ThreePart of the oxygen is further oxidized on platinum Pt while being absorbed into the active oxygen release / NOx absorbent 61 and combined with potassium K, sulfate ions SO._Four ^2-In the form of active oxygen release and NOx absorbent 61₂SO_FourIs generated. Thus, the active oxygen release / NOx absorbent 61 contains potassium nitrate KNO._ThreeAnd potassium sulfate K₂SO_FourIs generated.
[0074]
On the other hand, fine particles mainly made of carbon C are generated in the combustion chamber 5, and therefore these fine particles are contained in the exhaust gas. These fine particles contained in the exhaust gas are shown in FIG. 7 when the exhaust gas flows in the exhaust gas inflow passage 50 of the particulate filter 22 or when the exhaust gas flows from the exhaust gas inflow passage 50 toward the exhaust gas outflow passage 51. As shown at 62 in (B), it contacts and adheres to the surface of the carrier layer, for example, the surface of the active oxygen release / NOx absorbent 61.
[0075]
When the fine particles 62 adhere to the surface of the active oxygen release / NOx absorbent 61 in this way, the oxygen concentration at the contact surface between the fine particles 62 and the active oxygen release / NOx absorbent 61 decreases. When the oxygen concentration is lowered, a difference in concentration occurs between the active oxygen release / NOx absorbent 61 having a high oxygen concentration, and thus the oxygen in the active oxygen release / NOx absorbent 61 is separated from the fine particles 62 and the active oxygen release / NOx. It tries to move toward the contact surface with the absorbent 61. As a result, potassium nitrate KNO formed in the active oxygen release / NOx absorbent 61_ThreeIs decomposed into potassium K, oxygen O, and NO, oxygen O goes to the contact surface between the fine particles 62 and the active oxygen release / NOx absorbent 61, and NO is released from the active oxygen release / NOx absorbent 61 to the outside. . The NO released to the outside is oxidized on the platinum Pt on the downstream side and is again absorbed in the active oxygen release / NOx absorbent 61.
[0076]
On the other hand, potassium sulfate K formed in the active oxygen release / NOx absorbent 61 at this time₂SO_FourAlso potassium K, oxygen O and SO₂The oxygen O is directed to the contact surface between the fine particles 62 and the active oxygen release / NOx absorbent 61, and SO.₂Is released from the active oxygen release / NOx absorbent 61 to the outside. SO released to the outside₂Is oxidized on the platinum Pt on the downstream side and is again absorbed in the active oxygen release / NOx absorbent 61.
[0077]
On the other hand, oxygen O toward the contact surface between the fine particles 62 and the active oxygen release / NOx absorbent 61 is potassium nitrate KNO._ThreeAnd potassium sulfate K₂SO_FourIt is oxygen decomposed from a compound such as Oxygen O decomposed from the compound has high energy and has extremely high activity. Therefore, the oxygen directed toward the contact surface between the fine particles 62 and the active oxygen releasing / NOx absorbent 61 is active oxygen O. When these active oxygen O comes into contact with the fine particles 62, the fine particles 62 are oxidized within a short time without generating a luminous flame, and the fine particles 62 are completely extinguished. Therefore, the fine particles 62 are not deposited on the particulate filter 22.
[0078]
Alternatively, when the active oxygen O comes into contact with the fine particles 62, the oxidation action of the fine particles 62 is promoted, and the fine particles 62 are oxidized without emitting a luminous flame within a short time of several minutes to several tens of minutes. While the fine particles 62 are oxidized in this way, other fine particles adhere to the particulate filter 22 from one to the next. Therefore, in practice, a certain amount of fine particles are always deposited on the particulate filter 22, and some of the deposited fine particles are oxidized and removed. In this way, the fine particles 62 adhering to the particulate filter 22 are continuously burned without emitting a bright flame.
[0079]
Note that NOx is a nitrate ion NO in the active oxygen release / NOx absorbent 61 while repeatedly binding and separating oxygen atoms._Three ^-The active oxygen is generated during this period. The fine particles 62 are also oxidized by this active oxygen. Further, the fine particles 62 adhering to the particulate filter 22 in this manner are oxidized by the active oxygen O, but the fine particles 62 are also oxidized by oxygen in the exhaust gas. Also, when NOx is occluded by the active oxygen release / NOx absorbent 61, active oxygen is generated in the reaction process with oxygen, and the fine particles 62 are thereby oxidized.
[0080]
When the particulates deposited in a layered manner on the particulate filter 22 are combusted as in the prior art, the particulate filter 22 becomes red hot and burns with a flame. Combustion with such a flame cannot be continued unless the temperature is high, and therefore the temperature of the particulate filter 22 must be maintained at a high temperature in order to sustain the combustion with such a flame.
[0081]
On the other hand, in the present invention, the fine particles 62 are oxidized without generating a luminous flame as described above, and at this time, the surface of the particulate filter 22 does not become red hot. That is, in other words, in the present invention, the fine particles 62 are removed by oxidation at a considerably lower temperature than in the prior art. Therefore, the particulate removal action by oxidation of the particulate 62 that does not emit a luminous flame according to the present invention is completely different from the particulate removal action by the conventional combustion with a flame.
[0082]
Further, the particulate removal action by oxidation of the particulates is performed at a considerably low temperature. Therefore, the temperature of the particulate filter 22 does not rise so much, and therefore there is almost no risk that the particulate filter 22 will deteriorate. Further, since the particulates hardly accumulate on the particulate filter 22, there is little risk of ash that is a burning residue of particulates, and therefore the risk of clogging the particulate filter 22 is reduced.
[0083]
By the way, this clogging is mainly calcium sulfate CaSO._FourCaused by. That is, fuel and lubricating oil contain calcium Ca, and therefore, exhaust Ca contains calcium Ca. This calcium Ca is SO_ThreeIn the presence of calcium sulfate CaSO_FourIs generated. This calcium sulfate CaSO_FourIs solid and does not thermally decompose even at high temperatures. Therefore calcium sulfate CaSO_FourThis calcium sulfate CaSO_FourIf the pores of the particulate filter 22 are blocked by this, clogging occurs.
[0084]
However, in this case, if an alkali metal or alkaline earth metal having a higher ionization tendency than calcium Ca, such as potassium K, is used as the active oxygen release / NOx absorbent 61, SO diffuses into the active oxygen release / NOx absorbent 61._ThreeBinds potassium K and potassium sulfate K₂SO_FourCalcium Ca is SO_ThreeWithout passing through the partition wall 54 of the particulate filter 22 and flows into the exhaust gas outflow passage 51. Therefore, the pores of the particulate filter 22 are not clogged. Therefore, as described above, it is preferable to use an alkali metal or alkaline earth metal having higher ionization tendency than calcium Ca, that is, potassium K, lithium Li, cesium Cs, and barium Ba as the active oxygen release / NOx absorbent 61. Become.
[0085]
By the way, the platinum Pt and the active oxygen release / NOx absorbent 61 are activated as the temperature of the particulate filter 22 becomes higher. Therefore, the amount of active oxygen O that can be released by the active oxygen release / NOx absorbent 61 per unit time is the particulate. It increases as the temperature of the filter 22 increases. As a matter of course, the higher the temperature of the fine particles themselves, the easier they are removed by oxidation. Accordingly, the amount of fine particles that can be removed by oxidation without emitting a bright flame per unit time on the particulate filter 22 increases as the temperature of the particulate filter 22 increases.
[0086]
The solid line in FIG. 9 shows the amount G of fine particles that can be removed by oxidation without emitting a bright flame per unit time. In FIG. 9, the horizontal axis indicates the temperature TF of the particulate filter 22. FIG. 9 shows the amount G of fine particles that can be removed by oxidation when the unit time is 1 second, that is, 1 second, but any unit time such as 1 minute or 10 minutes can be adopted as this unit time. it can. For example, when 10 minutes is used as the unit time, the oxidizable and removable fine particle amount G per unit time represents the oxidizable and removable fine particle amount G per 10 minutes. Even in this case, the unit time on the particulate filter 22 is the unit time. As shown in FIG. 9, the amount G of fine particles that can be removed by oxidation without causing a bright flame per unit increases as the temperature of the particulate filter 22 increases.
[0087]
The amount of fine particles discharged from the combustion chamber 5 per unit time is referred to as discharged fine particle amount M. When the discharged fine particle amount M is smaller than the oxidizable and removable fine particle G, that is, in the region I in FIG. As soon as all the fine particles that have come into contact with the particulate filter 22, they are oxidized and removed on the particulate filter 22 without emitting a luminous flame in a short time.
[0088]
In contrast, when the amount M of discharged particulate is larger than the amount G of particulate that can be removed by oxidation, that is, in the region II of FIG. 9, the amount of active oxygen is insufficient to oxidize all the particulates. 8A to 8C show the state of oxidation of the fine particles in such a case.
[0089]
That is, when the amount of active oxygen is insufficient to oxidize all the fine particles, a part of the fine particles 62 is attached when the fine particles 62 adhere on the active oxygen releasing / NOx absorbent 61 as shown in FIG. Only a portion of the fine particles which are oxidized and not sufficiently oxidized remain on the carrier layer. Next, when the state where the amount of active oxygen is insufficient continues, the fine particles that have not been oxidized from one to the next remain on the carrier layer, and as a result, the surface of the carrier layer remains as shown in FIG. 8B. The fine particle portion 63 is covered.
[0090]
The residual fine particle portion 63 covering the surface of the carrier layer gradually changes to a carbonaceous material that is hardly oxidized, and thus the residual fine particle portion 63 tends to remain as it is. Further, when the surface of the carrier layer is covered with the residual fine particle portion 63, NO, SO by platinum Pt₂The active oxygen release action by the active oxygen release / NOx absorbent 61 is suppressed. As a result, as shown in FIG. 8C, other fine particles 64 are deposited one after another on the remaining fine particle portion 63. That is, the fine particles are deposited in a laminated form. Thus, when the fine particles are deposited in a laminated form, these fine particles are separated from the platinum Pt and the active oxygen release / NOx absorbent 61 so that even if the fine particles are easily oxidized, they are no longer oxidized by the active oxygen O. Therefore, further fine particles are deposited on the fine particles 64 one after another. That is, if the state where the amount M of discharged particulates is larger than the amount G of particulates that can be removed by oxidation continues, the particulates accumulate on the particulate filter 22 in a laminated form.
[0091]
As described above, in the region I in FIG. 9, the fine particles are oxidized on the particulate filter 22 within a short time without emitting a bright flame, and in the region II in FIG. 9, the fine particles are deposited on the particulate filter 22 in a laminated form. To do. Therefore, in order to prevent the fine particles from depositing on the particulate filter 22 in layers, it is desirable that the relationship between the discharged fine particle amount M and the fine particle amount G that can be removed by oxidation at all times is in the range of the region I.
[0092]
In practice, however, it is almost impossible to make the amount M of discharged particulates smaller than the amount G of particulates that can be removed by oxidation in all operating states. For example, when the engine is started, the temperature of the particulate filter 22 is usually low. Therefore, at this time, the amount M of normally discharged particulates is larger than the amount G of particulates that can be removed by oxidation. If the amount M of discharged particulates is larger than the amount G of particulates that can be removed by oxidation as immediately after the engine is started, particulates that have not been oxidized begin to remain on the particulate filter 22.
[0093]
Thus, depending on the operating conditions, the amount M of discharged particulates may be larger than the amount G of particulates that can be removed by oxidation, and the particulates may accumulate on the particulate filter 22 in a stacked manner.
[0094]
In order to oxidize and remove the deposited fine particles, the switching valve 71 disposed in the exhaust pipe 70 is switched. When the switching valve 71 is switched, the exhaust upstream side and the exhaust downstream side of the particulate filter 22 are reversed, and fine particles are released from the active oxygen and NOx are absorbed in the portion that was on the exhaust downstream side of the particulate filter 22 before switching. The active oxygen O is released on the surface of the agent 61 and the fine particles are oxidized and removed. A part of the released active oxygen O moves to the exhaust gas downstream side of the particulate filter 22 together with the exhaust gas, and oxidizes and removes the fine particles deposited there. Here, as described above, the fine particles are disturbed in both the forward flow direction and the reverse flow direction on both sides of the particulate filter 22 and move around on both sides of the particulate filter 22 or inside the substrate, and come into contact with the active points of the entire filter substrate and oxidize. Is done.
[0095]
When particulates that have not been oxidized in this manner are starting to accumulate on the particulate filter 22, the particulates are completely removed from the particulate filter 22 by reversing the exhaust upstream side and downstream side of the particulate filter 22. Oxidation can be removed.
[0096]
Further, when particulates are deposited on the particulate filter 22, the deposited particulates are oxidized without emitting a luminous flame by temporarily enriching the air-fuel ratio of a part or the whole of the exhaust gas. When the air-fuel ratio of the exhaust gas is made rich, that is, when the oxygen concentration in the exhaust gas is lowered, the active oxygen O is released from the active oxygen release / NOx absorbent 61 to the outside, and these active oxygen released at once. Fine particles deposited by O can be burned and removed in a short time without emitting a luminous flame.
The above is the fine particle purification mechanism utilizing the function of the active oxygen release / NOx absorbent as the active oxygen release agent.
[0097]
<NOx purification treatment with active oxygen release and NOx absorbent ... Function as NOx absorbent>
Next, the NOx purification action utilizing the function of the active oxygen release / NOx absorbent as the NOx absorbent will be described. The NOx absorbent functions as a NOx absorbent even if another alkali metal, alkaline earth metal, or rare earth is used as the NOx absorbent.
[0098]
It is considered that the NOx purification action of the active oxygen release / NOx absorbent is performed by the mechanism shown in FIG. In FIGS. 10A and 10B, reference numeral 60 indicates platinum Pt particles, and reference numeral 61 indicates an active oxygen release / NOx absorbent containing potassium K.
[0099]
First, when the air-fuel ratio of the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases, and as shown in FIG.₂Is O₂ ^-Or O^2-It adheres to the surface of platinum Pt. On the other hand, NO contained in the inflowing exhaust gas is O on the surface of platinum Pt.₂ ^-Or O^2-Reacts with NO₂(2NO + O₂→ 2NO₂).
[0100]
Then the generated NO₂Is oxidized in platinum Pt while being absorbed in the active oxygen release / NOx absorbent 61 and combined with potassium K, as shown in FIG._Three ^-The active oxygen release / NOx absorbent 61 diffuses in the form of In this way, NOx is absorbed into the active oxygen release / NOx absorbent 61.
[0101]
As long as the oxygen concentration in the inflowing exhaust gas is high, NO on the surface of platinum Pt₂Unless NO is absorbed and the NOx absorption capacity of the NOx absorbent 61 is saturated.₂Is absorbed in the active oxygen release / NOx absorbent 61 and nitrate ions NO._Three ^-Is generated.
[0102]
On the other hand, when the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or rich, the oxygen concentration in the inflowing exhaust gas decreases.₂Production amount decreases and the reaction proceeds in the reverse direction (NO_Three ^-→ NO₂) To release active oxygen and nitrate ion NO in the NOx absorbent 61_Three ^-Is NO₂Alternatively, it is released from the active oxygen release / NOx absorbent 61 in the form of NO. That is, when the oxygen concentration in the inflowing exhaust gas decreases, NOx is released from the active oxygen release / NOx absorbent 61.
[0103]
On the other hand, at this time, HC and CO in the exhaust gas are oxygen O on platinum Pt.₂ ^-Or O₂ ^-It reacts with and is oxidized. Further, NO released from the active oxygen release / NOx absorbent 61 due to a decrease in oxygen concentration in the inflowing exhaust gas.₂Alternatively, NO is reduced by reacting with unburned HC and CO as shown in FIG.₂It becomes.
[0104]
That is, HC and CO in the inflowing exhaust gas are first oxygen O on platinum Pt.₂ ^-Or O^2-Immediately reacts with and oxidizes, then oxygen O on platinum Pt.₂ ^-Or O^2-If HC and CO still remain after the consumption of NO, NOx released from the active oxygen release / NOx absorbent 61 and NOx discharged from the internal combustion engine by the HC and CO are N₂Reduced to
[0105]
In this way, NO on the surface of platinum Pt.₂Or when NO is no longer present, NO is released from the active oxygen release / NOx absorbent 61 to the next.₂Or NO is released and N₂To be reduced. Therefore, when the air-fuel ratio of the exhaust gas is made the stoichiometric air-fuel ratio or rich, NOx is released from the active oxygen release / NOx absorbent 61 within a short time, and N₂Reduced to
[0106]
Thus, when the air-fuel ratio of the exhaust gas becomes lean, NOx is absorbed by the active oxygen release / NOx absorbent 61, and when the air-fuel ratio of the exhaust gas is made the stoichiometric air-fuel ratio or rich, NOx is released by the active oxygen release / NOx absorbent 61. Released in a short time from N₂Reduced to Accordingly, NOx emission into the atmosphere can be prevented. Further, when the air-fuel ratio is repeatedly switched between lean and rich, as the amount of released active oxygen increases, the fine particles are easily oxidized and the oxidizable removal amount per unit time increases.
[0107]
If the air-fuel ratio is maintained lean, the surface of platinum Pt is covered with oxygen, and so-called oxygen poisoning of platinum Pt occurs. When such oxygen poisoning occurs, the oxidation effect on NOx is reduced, so that the NOx absorption efficiency is reduced, and thus the amount of active oxygen released from the active oxygen release / NOx absorbent 61 is reduced. However, when the air-fuel ratio is made rich, oxygen on the platinum Pt surface is consumed, so that oxygen poisoning is eliminated. Therefore, when the air-fuel ratio is switched from rich to lean, the oxidizing action on NOx is strengthened, so NOx is absorbed. The efficiency is increased, and thus the amount of active oxygen released from the active oxygen releasing / NOx absorbent 61 is increased.
[0108]
Accordingly, when the air-fuel ratio is maintained lean, the air-fuel ratio is temporarily switched from lean to rich occasionally, so that oxygen poisoning of platinum Pt is eliminated each time, so that active oxygen release when the air-fuel ratio is lean is performed. The amount increases, and thus the oxidation action of fine particles on the particulate filter 22 can be promoted.
[0109]
Cerium Ce takes in oxygen when the air-fuel ratio is lean (Ce₂O_Three→ 2CeO₂), Active oxygen is released when the air-fuel ratio becomes rich (2CeO)₂→ Ce₂O_Three) Has a function. Accordingly, when cerium Ce is used as the active oxygen release / NOx absorbent 61, when fine particles adhere to the particulate filter 22 when the air-fuel ratio is lean, the fine particles are oxidized by the active oxygen released from the active oxygen release / NOx absorbent 61. When the air-fuel ratio becomes rich, a large amount of active oxygen is released from the active oxygen release / NOx absorbent 61, so that the fine particles are oxidized. Accordingly, even when cerium Ce is used as the active oxygen release / NOx absorbent 61, the oxidation reaction of fine particles on the particulate filter 22 can be promoted if the air-fuel ratio is temporarily switched from lean to rich occasionally. Note that transition metal tin or the like can be used instead of cerium Ce.
[0110]
By the way, as described above, in this compression ignition type internal combustion engine, combustion is usually performed in a lean region much more than stoichiometric (theoretical air-fuel ratio, A / F = 14.6). The air-fuel ratio of the exhaust gas flowing into the exhaust gas 22 (that is, the exhaust gas flowing into the active oxygen release / NOx absorbent 61) is very lean, and NOx in the exhaust is absorbed by the active oxygen release / NOx absorbent 61, The amount of NOx released from the active oxygen release / NOx absorbent 61 is extremely small.
[0111]
Therefore, in a compression ignition type internal combustion engine, the reducing agent is supplied into the exhaust gas at a predetermined timing before the NOx absorption capacity of the active oxygen release / NOx absorbent 61 is saturated, thereby reducing the oxygen concentration in the exhaust gas. , NOx absorbed in the active oxygen release / NOx absorbent 61 is released and N₂It is necessary to reduce it.
[0112]
Therefore, in this embodiment, when the ECU 30 estimates the NOx amount absorbed by the active oxygen release / NOx absorbent 61 from the history of the operating state of the internal combustion engine, and the estimated NOx amount reaches a predetermined value set in advance. In addition, the air-fuel ratio of the exhaust gas is temporarily made rich to lower the oxygen concentration, and at the same time, the reducing agent is supplied. In this way, temporarily making the air-fuel ratio of the exhaust gas rich is called a rich spike.
[0113]
In this embodiment, a rich spike is realized by sub-injecting fuel into the cylinder during the expansion stroke or exhaust stroke of the internal combustion engine. The rich spike can also be realized by supplying fuel into the exhaust passage 70 upstream of the filter 22.
[0114]
In this way, by executing the rich spike at a predetermined timing before the NOx absorption capacity of the active oxygen release / NOx absorbent 61 is saturated, NOx in the exhaust gas can be continuously purified, and NOx is reduced. It can be prevented from being released into the atmosphere.
The above is the NOx purification mechanism utilizing the function of the active oxygen release / NOx absorbent 61 as the NOx absorbent.
[0115]
Therefore, when the active oxygen release / NOx absorbent 61 is used, when the air-fuel ratio of the exhaust gas flowing into the filter 22 is lean, NOx contained in the exhaust gas is absorbed by the active oxygen release / NOx absorbent 61, When the fine particles contained in the exhaust gas adhere to the active oxygen release / NOx absorbent 61, the fine particles are oxidized and removed in a short time by the active oxygen released from the active oxygen release / NOx absorbent 61. That is, at this time, it is possible to prevent both fine particles and NOx in the exhaust gas from being discharged into the atmosphere.
[0116]
On the other hand, when the air-fuel ratio of the exhaust gas flowing into the filter 22 becomes rich, NOx is released from the active oxygen release / NOx absorbent 61. This NOx is reduced by unburned HC and CO, and therefore NOx is not discharged into the atmosphere at this time as well. At this time, if fine particles are deposited on the filter 22, the fine particles are oxidized and removed by the active oxygen released from the active oxygen release / NOx absorbent 61.
[0117]
By the way, as described above, when the exhaust switching valve 71 is switched to switch the flow direction of the exhaust gas flowing through the filter 22 in order to promote the oxidation removal of fine particles in the filter 22, the valve body of the exhaust switching valve 71 is always in the neutral position. Switching operation is performed via. When the valve body is operating in the vicinity of the neutral position in the middle of the switching of the exhaust switching valve 71, the exhaust pipe 70 and the bypass passage 73 are directly connected. 70 flows through the bypass passage 73 without passing through the filter 22 and is released to the atmosphere.
[0118]
At this time, if the above-described rich spike for releasing and reducing NOx from the active oxygen releasing / NOx absorbent 61 is executed, the rich air-fuel ratio exhaust gas containing a large amount of hydrocarbons HC and carbon monoxide CO becomes active oxygen. Release / NOx absorbent 61 is not preferable because it may be released to the atmosphere without passing through.
[0119]
Therefore, in this embodiment, in order to prevent such a situation, when the switching timing of the exhaust gas flow by switching the exhaust switching valve 71 coincides with the execution timing of the rich spike, the exhaust switching valve 71 Switching was prioritized and execution of rich spask was prohibited, and simultaneous execution of these two processes was prohibited.
[0120]
Next, the exhaust gas flow switching control in this embodiment will be described with reference to the flowchart of FIG.
The flowchart shown in FIG. 11 shows an exhaust gas flow switching control routine. This exhaust gas flow switching control routine is stored in advance in the ROM 32 of the ECU 30, and is executed by the CPU 34 at regular intervals.
[0121]
<Step 101>
First, in step 101, the CPU 34 determines whether it is the switching timing of the exhaust gas switching valve 71. The switching condition of the exhaust switching valve 71 (hereinafter referred to as the exhaust gas flow switching condition) is, for example, during deceleration operation with a small amount of harmful components (such as particulates) in the exhaust gas, or the temperature of the filter 22 satisfies a predetermined condition. Or when the back pressure upstream of the filter 22 rises above a predetermined pressure, or when several of these conditions are met simultaneously.
[0122]
<Step 102>
If an affirmative determination is made in step 101, the CPU 34 proceeds to step 102 and determines whether or not it is the execution timing of the rich spike. In this embodiment, as described above, when the amount of NOx absorbed in the active oxygen release / NOx absorbent 61 carried on the filter 22 reaches a predetermined amount, the condition for executing the rich spike is satisfied. Assuming that rich spike is executed.
[0123]
<Step 103>
If the determination in step 102 is affirmative, the CPU 34 proceeds to step 103 and prohibits execution of the rich spike even at the execution timing of the rich spike.
[0124]
<Step 104>
Next, the CPU 34 proceeds to step 104 to execute switching of the exhaust switching valve 71 to switch the direction of the exhaust gas flow flowing through the filter 22 and to promote the oxidation removal of the particulates accumulated in the filter 22.
Even when a negative determination is made in step 102, the CPU 34 proceeds to step 104 and executes switching of the exhaust gas switching valve 71.
[0125]
In this series of steps from step 101 to step 104, when the switching timing of the exhaust switching valve 71 coincides with the rich spike execution timing, switching of the exhaust switching valve 71 is executed with priority over the rich spike. In other words, it means prohibiting the simultaneous execution of these two processes.
[0126]
<Step 105>
On the other hand, if a negative determination is made in step 101, the CPU 34 proceeds to step 105 and determines whether it is the execution timing of the rich spike. If a negative determination is made in step 105, the CPU 34 temporarily ends the execution of this routine.
[0127]
<Step 106>
If an affirmative determination is made in step 105, the CPU 34 proceeds to step 106, executes a rich spike, flows the rich air-fuel ratio exhaust gas through the filter 22, and is absorbed by the active oxygen release / NOx absorbent 61. NOx is released and N₂To reduce.
[0128]
In the embodiment described above, the active oxygen release agent and the NOx absorbent are supported on the particulate filter. However, in other embodiments, neither the active oxygen release agent nor the NOx absorbent is supported on the particulate filter. It's okay. In other words, when unburned fuel is supplied to the particulate filter, the unburned fuel is not supplied to the particulate filter, and it is avoided that the particulate filter bypasses the particulate filter and is discharged outside the vehicle. Therefore, the particulate filter is not limited to the one carrying the active oxygen release agent and the NOx absorbent.
[0129]
[Second Embodiment]
Next, a second embodiment of the exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with reference to the drawing of FIG. In the first embodiment described above, when the switching timing of the exhaust switching valve 71 coincides with the rich spike execution timing, the switching of the exhaust switching valve 71 is executed with priority over the rich spike. In the second embodiment, the rich spike is prioritized over the switching of the exhaust switching valve 71 in such a case.
[0130]
The exhaust gas flow switching control according to the second embodiment will be described with reference to the flowchart of FIG.
The flowchart shown in FIG. 12 shows an exhaust gas flow switching control routine. This exhaust gas flow switching control routine is stored in advance in the ROM 32 of the ECU 30, and is executed by the CPU 34 at regular intervals.
[0131]
<Step 201>
First, in step 201, the CPU 34 determines whether it is the execution timing of the rich spike. Note that the rich spike execution condition can be established in the same manner as in the first embodiment.
[0132]
<Step 202>
If an affirmative determination is made in step 201, the CPU 34 proceeds to step 202 and determines whether or not it is the switching timing of the exhaust gas switching valve 71. The exhaust gas flow switching condition can be the same as in the first embodiment.
[0133]
<Step 203>
If the determination in step 202 is affirmative, the CPU 34 proceeds to step 203 and prohibits execution of switching of the exhaust gas switching valve 71 even at the switching timing of the exhaust gas switching valve 71.
[0134]
<Step 204>
Next, the CPU 34 proceeds to step 204, executes a rich spike, causes the rich air-fuel ratio exhaust gas to flow through the filter 22, releases NOx absorbed in the active oxygen release / NOx absorbent 61, and N₂To reduce.
[0135]
Even if a negative determination is made in step 202, the CPU 34 proceeds to step 204 and executes rich spice.
[0136]
In this series of steps from step 201 to step 204, when the switching timing of the exhaust switching valve 71 coincides with the rich spike execution timing, the rich spike is executed with priority over the switching of the exhaust switching valve 71. In other words, it means prohibiting the simultaneous execution of these two processes.
[0137]
<Step 205>
On the other hand, if a negative determination is made in step 201, the CPU 34 proceeds to step 205 and determines whether it is the switching timing of the exhaust gas switching valve 71. If a negative determination is made in step 205, the CPU 34 temporarily ends the execution of this routine.
[0138]
<Step 206>
If an affirmative determination is made in step 205, the CPU 34 proceeds to step 206, executes the switching of the exhaust switching valve 71, switches the direction of the exhaust gas flow flowing through the filter 22, and removes particulates accumulated in the filter 22. Promotes oxidation removal.
[0139]
Also in the modification of this embodiment, a particulate filter in which no active oxygen release agent and NOx absorbent are supported can be used.
[0140]
[Third Embodiment]
Next, a third embodiment of the exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with reference to the drawing of FIG.
[0141]
In the exhaust gas purification apparatus according to the first embodiment described above, fine particles in the exhaust gas should not accumulate on the filter 22, but depending on the operating state of the internal combustion engine (for example, during deceleration operation), the fine particles in the filter 22 In some cases, the oxidation removal performance of fine particles may be deteriorated when the oxidation removal is not sufficiently performed or the temperature of the exhaust gas is low. In such a case, an exhaust gas flow control method (hereinafter referred to as filter bypass control) of bypassing the filter 22 and flowing the exhaust gas in order to prevent accumulation of more than a set amount of fine particles on the filter 22 is also considered. It is done.
[0142]
When the exhaust gas is flown by bypassing the filter 22 by executing this filter bypass control, if rich spike for NOx purification is executed, the rich sky containing a large amount of hydrocarbon HC and carbon monoxide CO is still obtained. The exhaust gas having a fuel ratio is released into the atmosphere without passing through the activated carbon release / NOx absorbent 61, which is not preferable.
[0143]
Therefore, in the third embodiment, when the rich spike execution timing comes during the execution of the filter bypass control, priority is given to the execution of the rich spike and the exhaust gas flows to the filter 22 during the execution period of the rich spike. Therefore, the exhaust gas switching valve 71 is switched.
[0144]
The exhaust gas flow switching control in the third embodiment will be described with reference to the flowchart of FIG.
The flowchart shown in FIG. 13 shows an exhaust gas flow switching control routine. This exhaust gas flow switching control routine is stored in advance in the ROM 32 of the ECU 30, and is executed by the CPU 34 at regular intervals.
[0145]
<Step 301>
First, in step 301, the CPU 34 determines whether or not a filter bypass control execution condition is satisfied. Whether or not the filter bypass control execution condition is satisfied can be determined from the operating state of the internal combustion engine, for example, during deceleration operation.
[0146]
<Step 302>
If an affirmative determination is made in step 301, the CPU 34 proceeds to step 302 and determines whether it is the execution timing of the rich spike. Note that the rich spike execution condition can be established in the same manner as in the first embodiment.
[0147]
<Step 303>
If an affirmative determination is made in step 302, the CPU 34 proceeds to step 303, and even if the filter bypass control execution condition is satisfied, the exhaust gas switching valve is set so that the exhaust gas flows through the filter 22 without executing the filter bypass control. 71 is switched. In other words, the exhaust gas is prevented from flowing around the filter 22 (valve non-neutral position).
[0148]
<Step 304>
Next, the CPU 34 proceeds to step 304, executes a rich spike, causes the rich air-fuel ratio exhaust gas to flow through the filter 22, releases NOx absorbed in the active oxygen release / NOx absorbent 61, and N₂To reduce.
[0149]
In this series of flow from step 301 to step 304, when the rich spike execution timing comes during execution of the filter bypass control, the filter vice control is interrupted and the rich spike is executed so that the exhaust gas flows through the filter 22. In other words, it means prohibiting the simultaneous execution of these two processes.
[0150]
<Step 305>
On the other hand, if a negative determination is made in step 302, the CPU 34 proceeds to step 305 and executes filter bypass control to switch the exhaust switching valve 71 to the neutral position so that the exhaust gas flows around the filter 22. This prevents the particulates from accumulating on the filter 22 and terminates the execution of this routine. If a negative determination is made in step 301, the CPU 34 temporarily ends the execution of this routine. That is, in this case, the exhaust switching valve 71 is switched according to normal control.
[0151]
The present invention is also valid when a noble metal catalyst such as platinum Pt and a NOx absorbent are supported on the carrier layer formed on the filter 22. However, in this case, the solid line indicating the amount G of fine particles that can be removed by oxidation moves slightly to the right as compared with the solid line shown in FIG. In this case, NO held on the surface of platinum Pt.₂Or SO_ThreeActive oxygen is released from
In addition, as the active oxygen release agent, NO₂Or SO_ThreeAnd adsorbed NO.₂Or SO_ThreeA catalyst capable of releasing active oxygen from the catalyst can also be used.
[0152]
Also in the modification of this embodiment, a particulate filter in which no active oxygen release agent and NOx absorbent are supported can be used.
[0153]
[Fourth Embodiment]
Hereinafter, a fourth embodiment of the exhaust gas purification apparatus for an internal combustion engine of the present invention will be described. The configuration of the present embodiment is the same as the configuration of the first embodiment except that the catalyst for oxidizing the fine particles is not limited to the active oxygen release agent, and the NOx absorbent is not supported on the particulate filter. It is almost the same.
[0154]
FIG. 14 is a flowchart showing an operation control method of the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment. The routine shown in FIG. 14 is executed at predetermined time intervals during the operation period of the internal combustion engine. As shown in FIG. 14, when this routine is started, it is first determined in step 401 whether or not it is the switching timing of the exhaust gas switching valve 71. When YES, the routine proceeds to step 402, and when NO, this routine is terminated. For example, YES is determined at the time of engine deceleration operation after a predetermined period has elapsed since the exhaust switching valve 71 was switched. In step 402, it is determined whether low-temperature combustion, which will be described later, is being performed. If yes, then continue with step 403, otherwise continue with step 404. In step 403, switching of the exhaust gas switching valve 71 is prohibited. That is, in order to avoid that the exhaust gas switching valve 71 is disposed at the bypass position (the one-dot chain line in FIG. 3), the exhaust gas switching valve 71 has a forward flow position (dashed line in FIG. 3) and a reverse flow position (solid line in FIG. 3). Switching between is prohibited. On the other hand, in step 404, switching of the exhaust switching valve 71 is executed. That is, the exhaust gas switching valve 71 is switched from the forward flow position to the reverse flow position, or from the reverse flow position to the forward flow position. At that time, the exhaust gas switching valve 71 is passed through the bypass position.
[0155]
Hereinafter, the low-temperature combustion described above will be described. In the internal combustion engine shown in FIG. 1, as the EGR rate (EGR gas amount / (EGR gas amount + intake air amount)) increases, the amount of smoke generated gradually increases and reaches a peak, and the EGR rate is further increased. This time, the amount of smoke generated decreases rapidly. This will be described with reference to FIG. 15 showing the relationship between the EGR rate and smoke when the degree of cooling of the EGR gas is changed. In FIG. 15, curve A shows the case where EGR gas is strongly cooled and the EGR gas temperature is maintained at about 90 ° C., and curve B shows the case where EGR gas is cooled by a small cooling device. Curve C shows the case where the EGR gas is not forcibly cooled.
[0156]
As shown by curve A in FIG. 15, when the EGR gas is cooled strongly, the amount of smoke generated peaks when the EGR rate is slightly lower than 50%. In this case, the EGR rate is increased to about 55% or more. If this is done, smoke will hardly occur. On the other hand, as shown by curve B in FIG. 15, when the EGR gas is slightly cooled, the amount of smoke generated peaks when the EGR rate is slightly higher than 50%. In this case, the EGR rate is approximately 65% or more. If it is made, smoke will hardly occur. Further, as shown by the curve C in FIG. 15, when the EGR gas is not forcibly cooled, the amount of smoke generated reaches a peak when the EGR rate is around 55%. In this case, the EGR rate is approximately 70%. If it is more than a percentage, smoke is hardly generated. As described above, when the EGR gas ratio is 55% or more, smoke is not generated because the endothermic action of the EGR gas does not cause the temperature of the fuel and the surrounding gas to be so high, that is, low-temperature combustion is performed. This is because hydrocarbons do not grow to soot.
[0157]
This low-temperature combustion has a feature that the amount of NOx generated can be reduced while suppressing the generation of smoke regardless of the air-fuel ratio. That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but the combustion temperature is suppressed to a low temperature, so that the excessive fuel does not grow to the soot, and thus smoke does not occur. At this time, only a very small amount of NOx is generated. On the other hand, even when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is produced if the combustion temperature is high, but the combustion temperature is suppressed to a low temperature under low-temperature combustion. Smoke does not occur at all, and only a very small amount of NOx is generated.
[0158]
On the other hand, when this low-temperature combustion is performed, the temperature of the fuel and the surrounding gas decreases, but the exhaust gas temperature increases. This will be described with reference to FIGS. 16 (A) and 16 (B). The solid line in FIG. 16A shows the relationship between the average gas temperature Tg in the combustion chamber 5 and the crank angle when low-temperature combustion is performed, and the broken line in FIG. 16A shows normal combustion. The relationship between the average gas temperature Tg in the combustion chamber 5 and the crank angle is shown. The solid line in FIG. 16B shows the relationship between the fuel and the surrounding gas temperature Tf and the crank angle when low-temperature combustion is performed, and the broken line in FIG. 16B shows normal combustion. The relationship between the fuel and the surrounding gas temperature Tf when broken and the crank angle is shown.
[0159]
When low-temperature combustion is performed, the amount of EGR gas is larger than when normal combustion is performed. Therefore, as shown in FIG. 16A, before compression top dead center, that is, during the compression process, a solid line The average gas temperature Tg at the time of low-temperature combustion indicated by is higher than the average gas temperature Tg at the time of normal combustion indicated by a broken line. At this time, as shown in FIG. 16B, the fuel and the surrounding gas temperature Tf are substantially the same as the average gas temperature Tg. Next, combustion is started in the vicinity of the compression top dead center. In this case, when low-temperature combustion is being performed, as shown by the solid line in FIG. 16B, the fuel and the surrounding gas temperature Tf are absorbed by the endothermic action of the EGR gas. It wo n’t be that expensive. On the other hand, when normal combustion is performed, since a large amount of oxygen exists around the fuel, the fuel and the surrounding gas temperature Tf become extremely high as shown by the broken line in FIG. . In this way, when normal combustion is performed, the temperature of the fuel and the surrounding gas temperature Tf is considerably higher than when low temperature combustion is performed, but the temperature of the other gases which occupy most is low temperature combustion. Therefore, the average gas in the combustion chamber 5 in the vicinity of the compression top dead center as shown in FIG. 16 (A) is lower than that in the case where the normal combustion is performed. The temperature Tg is higher when low-temperature combustion is performed than when normal combustion is performed. As a result, as shown in FIG. 22 (A), the burned gas temperature in the combustion chamber 5 after the completion of combustion is higher when low temperature combustion is performed than when normal combustion is performed. Therefore, when the low temperature combustion is performed, the exhaust gas temperature becomes high.
[0160]
When low-temperature combustion is performed in this way, the amount of smoke generated, that is, the amount of discharged particulates decreases, and the exhaust gas temperature rises. Therefore, switching from normal combustion to low temperature combustion during engine operation can reduce the amount of discharged particulates and raise the temperature of the particulate filter 22. On the other hand, when switching from low temperature combustion to normal combustion, the temperature of the particulate filter 22 decreases. However, at this time, the amount of discharged fine particles increases. In any case, the amount of discharged particulates and the temperature of the particulate filter 22 can be controlled by switching between normal combustion and low temperature combustion.
[0161]
By the way, when the required torque TQ of the engine is increased, that is, when the fuel injection amount is increased, the temperature of the fuel and the surrounding gas at the time of combustion is increased, so that it is difficult to perform low temperature combustion. That is, low-temperature combustion can be performed only when the engine is in a low load operation where the amount of heat generated by combustion is relatively small. In FIG. 17, an area I ′ indicates an operation area in which the first combustion in which the amount of inert gas in the combustion chamber 5 is larger than the amount of inert gas at which the amount of soot reaches a peak, that is, low temperature combustion can be performed. Region II ′ shows the second combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas in which the amount of soot reaches a peak, that is, the operating region in which only normal combustion can be performed. . FIG. 18 shows the target air-fuel ratio A / F when low temperature combustion is performed in the operation region I ′, and FIG. 19 shows the opening of the throttle valve 17 according to the required torque TQ when low temperature combustion is performed in the operation region I ′. , The opening degree of the EGR control valve 25, the EGR rate, the air-fuel ratio, the injection start timing θS, the injection completion timing θE, and the injection amount. FIG. 19 also shows the opening degree of the throttle valve 17 during normal combustion performed in the operation region II ′. 18 and 19, it is understood that when the low temperature combustion is performed in the operation region I ′, the EGR rate is 55% or more and the air-fuel ratio A / F is a lean air-fuel ratio of about 15.5 to 18. . As described above, when low-temperature combustion is performed in the operation region I ', smoke is hardly generated even if the air-fuel ratio is made rich.
[0162]
That is, in this embodiment, during low temperature combustion in which exhaust gas having a relatively small exhaust gas air-fuel ratio is flowing, switching of the exhaust switching valve 11 is prohibited in step 403, and accordingly, the exhaust switching valve 11 is disposed at the bypass position. Doing so is also prohibited. On the other hand, when the exhaust gas having a relatively large exhaust gas air-fuel ratio is flowing, except during the low temperature combustion, the switching of the exhaust switching valve 11 is executed in step 404, and accordingly, the exhaust switching valve 11 passes the bypass position. Will be. Although not shown, when the switching timing of the exhaust switching valve 11 is reached during low temperature combustion in which exhaust gas having a relatively small exhaust gas air-fuel ratio is flowing, the combustion is first performed in a state where switching of the exhaust switching valve 11 is prohibited. Is switched from low-temperature combustion to normal combustion to increase the exhaust gas air-fuel ratio, and then the switching of the exhaust gas switching valve 11 is executed as in step 404. As described above, the low-temperature combustion can be performed at the time of engine low load operation, but it is also possible to perform low-temperature combustion to recover the particulate filter 22 when the particulate filter 22 is poisoned with SOx.
[0163]
According to the present embodiment, it is prohibited to dispose the exhaust switching valve 11 in the bypass position in step 403 during low temperature combustion in which exhaust gas having a relatively small exhaust gas air-fuel ratio flows, so HC, CO, unburned During low-temperature combustion in which exhaust gas having a relatively small exhaust gas air-fuel ratio including fuel or the like flows, the exhaust gas is bypassed without passing through the particulate filter 22 and is prevented from being discharged into the atmosphere. be able to.
[0164]
[Fifth Embodiment]
Hereinafter, a fifth embodiment of the exhaust gas purification apparatus for an internal combustion engine of the present invention will be described. The configuration of the present embodiment is substantially the same as the configuration of the first embodiment, except that the catalyst for oxidizing the fine particles is not limited to the active oxygen release agent. That is, in the exhaust gas purification apparatus for an internal combustion engine of the present embodiment, the NOx absorbent is carried on the particulate filter.
[0165]
The operation control method of the exhaust gas purification apparatus for the internal combustion engine of the present embodiment is substantially the same as the operation control method of the fourth embodiment shown in FIG. That is, in the present embodiment, switching of the exhaust gas switching valve 11 is prohibited as in step 403 at the time of low temperature combustion in which exhaust gas having a relatively small exhaust gas air-fuel ratio flows when NOx should be released from the NOx absorbent. Accordingly, it is also prohibited to place the exhaust gas switching valve 11 in the bypass position. On the other hand, when there is no need to release NOx from the NOx absorbent and the exhaust gas having a relatively large exhaust gas air-fuel ratio is flowing at a time other than low temperature combustion, switching of the exhaust gas switching valve 11 is executed in the same manner as in step 404. Accordingly, the exhaust gas switching valve 11 is allowed to pass through the bypass position.
[0166]
According to this embodiment, since the exhaust gas air-fuel ratio is relatively small and the NOx absorbent is releasing NOx, it is prohibited to place the exhaust switching valve 11 in the bypass position during low temperature combustion. Exhaust gas for releasing NOx from the exhaust gas, when exhaust gas having a relatively small exhaust gas air-fuel ratio including HC, CO, unburned fuel, etc. flows, the exhaust gas passes through the particulate filter 22 It is possible to avoid being bypassed and discharged into the atmosphere without being performed.
[0167]
[Sixth Embodiment]
Hereinafter, a sixth embodiment of the exhaust gas purification apparatus for an internal combustion engine of the present invention will be described. The configuration of the present embodiment is the same as the configuration of the first embodiment except that the catalyst for oxidizing the fine particles is not limited to the active oxygen release agent, and the NOx absorbent is not supported on the particulate filter. It is almost the same.
[0168]
FIG. 20 is a flowchart showing an operation control method of the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment. The routine shown in FIG. 20 is executed at predetermined time intervals during the operation period of the internal combustion engine. As shown in FIG. 20, when this routine is started, it is first determined in step 401 whether or not it is the switching timing of the exhaust switching valve 71. If YES, the routine proceeds to step 501, and if NO, this routine is terminated. For example, YES is determined at the time of engine deceleration operation after a predetermined period has elapsed since the exhaust switching valve 71 was switched. In step 501, it is determined whether or not low-temperature combustion is being performed at an air-fuel ratio of 8 to 24. If yes, then continue with step 403, otherwise continue with step 404. In step 403, switching of the exhaust gas switching valve 71 is prohibited. That is, in order to avoid that the exhaust gas switching valve 71 is disposed at the bypass position (the one-dot chain line in FIG. 3), the exhaust gas switching valve 71 has a forward flow position (dashed line in FIG. 3) and a reverse flow position (solid line in FIG. 3). Switching between is prohibited. On the other hand, in step 404, switching of the exhaust switching valve 71 is executed. That is, the exhaust gas switching valve 71 is switched from the forward flow position to the reverse flow position, or from the reverse flow position to the forward flow position. At that time, the exhaust gas switching valve 71 is passed through the bypass position.
[0169]
That is, in the present embodiment, during low-temperature combustion under the air-fuel ratio 8 to 24 where the exhaust gas having a relatively small exhaust gas air-fuel ratio is flowing, switching of the exhaust gas switching valve 11 is prohibited in step 403, and accordingly Arranging the exhaust gas switching valve 11 in the bypass position is also prohibited. On the other hand, at times other than during low-temperature combustion under the air-fuel ratio 8 to 24 where exhaust gas having a relatively large exhaust gas air-fuel ratio is flowing, the switching of the exhaust switching valve 11 is executed in step 404, and accordingly the exhaust gas is discharged. The switching valve 11 is allowed to pass through the bypass position. Although not shown, when the switching timing of the exhaust switching valve 11 is reached during low temperature combustion under the air-fuel ratio 8 to 24 where the exhaust gas having a relatively small exhaust gas air-fuel ratio flows, first, the exhaust switching valve 11 The combustion is switched from low temperature combustion under an air fuel ratio of 8 to 24 to normal combustion to increase the exhaust gas air fuel ratio, and then the exhaust gas switching valve 11 is switched as in step 404. Executed. Low-temperature combustion under an air-fuel ratio of 8 to 24 can be executed during low load operation in the engine, but when the particulate filter 22 is poisoned with SOx, the air-fuel ratio of 8 to 24 is recovered in order to recover the particulate filter 22. It is also possible to carry out a low temperature combustion underneath.
[0170]
According to the present embodiment, it is prohibited to place the exhaust gas switching valve 11 in the bypass position in step 403 during low-temperature combustion under the air-fuel ratio 8 to 24 where the exhaust gas having a relatively small exhaust gas air-fuel ratio flows. Therefore, the exhaust gas passes through the particulate filter 22 at the time of low-temperature combustion under the air-fuel ratio 8 to 24 where the exhaust gas having a relatively small exhaust gas air-fuel ratio including HC, CO, unburned fuel, etc. flows. It is possible to avoid being bypassed and discharged into the atmosphere without being performed.
[0171]
[Seventh Embodiment]
Hereinafter, a seventh embodiment of the exhaust gas purification apparatus for an internal combustion engine of the present invention will be described. The configuration of the present embodiment is substantially the same as the configuration of the first embodiment, except that the catalyst for oxidizing the fine particles is not limited to the active oxygen release agent. That is, in the exhaust gas purification apparatus for an internal combustion engine of the present embodiment, the NOx absorbent is carried on the particulate filter.
[0172]
The operation control method of the exhaust gas purification apparatus for the internal combustion engine of the present embodiment is substantially the same as the operation control method of the sixth embodiment shown in FIG. That is, in this embodiment, when NOx is to be released from the NOx absorbent and when low-temperature combustion is performed under an air-fuel ratio 8 to 24 where exhaust gas having a relatively small exhaust gas air-fuel ratio flows, the same as step 403 Therefore, switching of the exhaust gas switching valve 11 is prohibited, and accordingly, the exhaust gas switching valve 11 is also prohibited from being placed in the bypass position. On the other hand, it is not necessary to release NOx from the NOx absorbent, and the exhaust gas is exhausted in the same manner as in step 404 except when the combustion is at low temperature under the air-fuel ratio 8 to 24 where the exhaust gas having a relatively large exhaust gas air-fuel ratio flows. Switching of the switching valve 11 is executed, and accordingly, the exhaust switching valve 11 is passed through the bypass position.
[0173]
According to the present embodiment, the exhaust gas switching valve 11 is arranged at the bypass position at the time of low-temperature combustion under the air-fuel ratios 8 to 24 where the exhaust gas air-fuel ratio is relatively small and the NOx absorbent releases NOx. Therefore, when exhaust gas for releasing NOx from the NOx absorbent and having a relatively small exhaust gas air-fuel ratio including HC, CO, unburned fuel, etc. is flowing, It can be avoided that the exhaust gas is bypassed without passing through the particulate filter 22 and discharged into the atmosphere.
[0174]
[Eighth Embodiment]
Hereinafter, an eighth embodiment of the exhaust emission control device for an internal combustion engine of the present invention will be described. The configuration of the present embodiment is the same as the configuration of the first embodiment except that the catalyst for oxidizing the fine particles is not limited to the active oxygen release agent, and the NOx absorbent is not supported on the particulate filter. It is almost the same.
[0175]
FIG. 21 is a flowchart showing an operation control method of the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment. The routine shown in FIG. 21 is executed at predetermined time intervals during the operation period of the internal combustion engine. As shown in FIG. 21, when this routine is started, it is first determined in step 401 whether or not it is the switching timing of the exhaust gas switching valve 71. When YES, the routine proceeds to step 402, and when NO, this routine is terminated. For example, YES is determined at the time of engine deceleration operation after a predetermined period has elapsed since the exhaust switching valve 71 was switched. In step 402, it is determined whether low-temperature combustion is being performed. If YES, the process proceeds to step 601, and if NO, the process proceeds to step 404. In step 601, whether or not the exhaust gas air-fuel ratio is lean based on the output value of an air-fuel ratio sensor (not shown) for detecting the exhaust gas air-fuel ratio, which is the air-fuel ratio of the exhaust gas flowing into the particulate filter 22. Is determined. If NO, the process proceeds to step 403, and if YES, the process proceeds to step 404. In step 403, switching of the exhaust gas switching valve 71 is prohibited. That is, in order to avoid that the exhaust gas switching valve 71 is disposed at the bypass position (the one-dot chain line in FIG. 3), the exhaust gas switching valve 71 has a forward flow position (dashed line in FIG. 3) and a reverse flow position (solid line in FIG. 3). Switching between is prohibited. On the other hand, in step 404, switching of the exhaust switching valve 71 is executed. That is, the exhaust gas switching valve 71 is switched from the forward flow position to the reverse flow position, or from the reverse flow position to the forward flow position. At that time, the exhaust gas switching valve 71 is passed through the bypass position.
[0176]
That is, in this embodiment, during low temperature combustion where the exhaust gas air-fuel ratio is stoichiometric or rich, switching of the exhaust switching valve 11 is prohibited in step 403, and accordingly, the exhaust switching valve 11 is disposed at the bypass position. Is also prohibited. On the other hand, when the exhaust gas air / fuel is lean or when it is not during low-temperature combustion, the switching of the exhaust switching valve 11 is executed in step 404, and accordingly, the exhaust switching valve 11 passes the bypass position. Will be. Although not shown, when the switching timing of the exhaust switching valve 11 is reached during low temperature combustion in which the exhaust gas air-fuel ratio is stoichiometric or rich, the combustion is first performed in a state where switching of the exhaust switching valve 11 is prohibited. The exhaust gas air-fuel ratio is increased by switching from the combustion to the normal combustion, and then the switching of the exhaust gas switching valve 11 is executed as in step 404. The low-temperature combustion can be performed at the time of engine low load operation, but it is also possible to execute low-temperature combustion to recover the particulate filter 22 when the particulate filter 22 is poisoned with SOx.
[0177]
According to the present embodiment, since the exhaust gas switching valve 11 is prohibited from being placed in the bypass position in step 403 during low temperature combustion when the exhaust gas air-fuel ratio is stoichiometric or rich, HC, CO, unburned fuel, etc. It is possible to avoid that the exhaust gas is bypassed without passing through the particulate filter 22 and discharged into the atmosphere during low temperature combustion in which exhaust gas having a relatively small exhaust gas air-fuel ratio flows. it can.
[0178]
[Ninth Embodiment]
Hereinafter, a ninth embodiment of the exhaust gas purification apparatus for an internal combustion engine of the present invention will be described. The configuration of the present embodiment is substantially the same as the configuration of the first embodiment, except that the catalyst for oxidizing the fine particles is not limited to the active oxygen release agent. That is, in the exhaust gas purification apparatus for an internal combustion engine of the present embodiment, the NOx absorbent is carried on the particulate filter.
[0179]
The operation control method of the exhaust gas purification apparatus for the internal combustion engine of the present embodiment is substantially the same as the operation control method of the eighth embodiment shown in FIG. That is, in this embodiment, when NOx should be released from the NOx absorbent and at low temperature combustion where the exhaust gas air-fuel ratio is stoichiometric or rich, switching of the exhaust gas switching valve 11 is prohibited as in step 403, Accordingly, it is also prohibited to place the exhaust gas switching valve 11 in the bypass position. On the other hand, when there is no need to release NOx from the NOx absorbent and the exhaust gas air-fuel ratio is lean, or other than during low-temperature combustion, switching of the exhaust gas switching valve 11 is executed as in step 404, Accordingly, the exhaust gas switching valve 11 is allowed to pass through the bypass position.
[0180]
According to this embodiment, since the exhaust gas air-fuel ratio is stoichiometric or rich and the NOx absorbent is releasing NOx, it is prohibited to place the exhaust gas switching valve 11 in the bypass position during low temperature combustion. When exhaust gas for releasing NOx from the agent and having a relatively small exhaust gas air-fuel ratio including HC, CO, unburned fuel, etc. flows, the exhaust gas passes through the particulate filter 22. Bypassing without passing, it is possible to avoid being discharged into the atmosphere.
[0181]
[Tenth embodiment]
Hereinafter, a tenth embodiment of the exhaust gas purification apparatus for an internal combustion engine of the present invention will be described. The configuration of the present embodiment is substantially the same as the configuration of the first embodiment, except that the catalyst for oxidizing the fine particles is not limited to the active oxygen release agent. That is, in the exhaust gas purification apparatus for an internal combustion engine of the present embodiment, the NOx absorbent is carried on the particulate filter.
[0182]
In this embodiment, when the particulate oxidation performance by the particulate filter 22 is lower than a predetermined level, the exhaust gas switching valve 11 is normally disposed at the bypass position. The threshold value as the predetermined level may be set to a value indicating that the particulate oxidation performance by the particulate filter 22 has actually decreased, or the particulate oxidation reaction by the particulate filter 22 has not yet decreased. However, you may set to the value which shows that there exists a possibility that it may fall. On the other hand, even when the particulate oxidation performance by the particulate filter 22 is lower than the predetermined level, it is prohibited to dispose the exhaust switching valve 11 in the bypass position when NOx should be released from the NOx absorbent. Is done.
[0183]
According to the present embodiment, normally, when the oxidation performance of particulates by the particulate filter 22 is lower than a predetermined level, particulates that may contain particulates pass through the particulate filter 22 as the particulates pass through the particulate filter 22. It is possible to suppress an increase in the amount of fine particles deposited on the filter 22. In addition, even when the particulate oxidation performance by the particulate filter 22 is lower than the predetermined level, when NOx should be released from the NOx absorbent, HC, CO are used to release NOx from the NOx absorbent. As the exhaust gas containing unburned fuel and the like bypasses the particulate filter 22, it can be avoided that the exhaust gas is discharged into the atmosphere as it is.
[0186]
【The invention's effect】
  According to the first inventionIn order to improve the particulate oxidation removal capability by the filter, when the unburned fuel is supplied to the filter, the unburned fuel is avoided from being bypassed and discharged outside the vehicle without being supplied to the filter. be able to.
[0187]
  Also,According to the second invention,Oxidation performance of fine particles in a filterWhereWhen the level is lower than the constant level, the exhaust gas flows around the filter, so that it is possible to prevent fine particles of a set value or more from accumulating on the filter.
[0188]
  further,According to the second inventionWhen the NOx is released from the NOx absorbent, the bypass prohibiting means prohibits exhaust gas from flowing around the filter, so that the particulate oxidation performance in the filter is lower than the predetermined level. Even in such a case, the exhaust gas always flows through the filter, so that the exhaust gas controlled to the stoichiometric or rich air-fuel ratio to release NOx from the NOx absorbent does not pass through the filter and remains untreated. It can be prevented from being released as it is.
[0189]
  According to the third to sixth inventionsExhaust gas with relatively small exhaust gas air-fuel ratio, including HC, CO, unburned fuel, etc.IsBypassing without passing through the particulate filter, it is possible to avoid being discharged into the atmosphere.
[0190]
  According to the seventh invention,Exhaust gas for releasing NOx from NOx absorbent and having relatively small exhaust gas air-fuel ratio including HC, CO, unburned fuel, etc.IsBypassing without passing through the particulate filter, it is possible to avoid being discharged into the atmosphere.
[0191]
  Moreover, according to the eighth invention, lowExhaust gas exhausted from the combustion chamber during hot combustion and having a relatively small exhaust gas air-fuel ratio including HC, CO, unburned fuel, etc.IsBypassing without passing through the particulate filter, it is possible to avoid being discharged into the atmosphere.
[0192]
  According to the ninth invention,, During SOx poisoning recovery, NOx release, or engine low load operationLowExhaust gas containing HC, CO, unburned fuel, etc. discharged from the combustion chamber during warm combustionIsBypassing without passing through the particulate filter, it is possible to avoid being discharged into the atmosphere.
[0193]
  According to the tenth invention,Usually, when the particulate oxidation performance of the particulate filter is lower than a predetermined level, the amount of particulate deposition on the particulate filter increases as exhaust gas that may contain particulates passes through the particulate filter. In the case where NOx should be released from the NOx absorbent, the exhaust gas containing HC, CO, unburned fuel, etc. bypasses the particulate filter in order to release NOx from the NOx absorbent. Accordingly, the exhaust gas can be avoided from being discharged into the atmosphere as it is.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine.
FIG. 2 is a view showing a required torque of the engine.
FIG. 3 is a top view showing the exhaust emission control device.
FIG. 4 is a front view showing the exhaust emission control device.
5A is an image diagram showing a state in which particulates are deposited on a filter substrate, and FIG. 5B is an image diagram showing a state in which particulates are disturbed by forward and backward flow of exhaust gas.
FIG. 6 is a diagram showing a particulate filter.
FIG. 7 is a conceptual diagram showing the oxidizing action of fine particles.
FIG. 8 is a conceptual diagram showing the deposition action of fine particles.
FIG. 9 is a graph showing the relationship between the amount of fine particles that can be removed by oxidation and the temperature of the particulate filter.
FIG. 10 is a conceptual diagram showing NOx purification action.
FIG. 11 is a flowchart showing exhaust gas flow switching control in the first embodiment.
FIG. 12 is a flowchart showing exhaust gas flow switching control in the second embodiment.
FIG. 13 is a flowchart showing exhaust gas flow switching control in the third embodiment.
FIG. 14 is a flowchart showing an operation control method for an exhaust gas purification apparatus for an internal combustion engine according to a fourth embodiment.
FIG. 15 is a diagram showing the amount of smoke generated.
FIG. 16 is a diagram showing gas temperature and the like in the combustion chamber.
FIG. 17 is a diagram showing operation regions I ′ and II ′.
FIG. 18 is a diagram showing an air-fuel ratio A / F.
FIG. 19 is a diagram showing changes in the throttle valve opening and the like.
FIG. 20 is a flowchart showing an operation control method for an exhaust gas purification apparatus for an internal combustion engine according to a sixth embodiment.
FIG. 21 is a flowchart showing an operation control method of an exhaust gas purification apparatus for an internal combustion engine according to an eighth embodiment.
[Explanation of symbols]
6 ... Fuel injection valve
22 ... Particulate filter
30 ... ECU
61 ... Active oxygen release / NOx absorbent (NOx absorbent, active oxygen release agent)
71 ... Exhaust selector valve
75 ... Control means

Claims (10)

A filter that collects particulates in exhaust gas for a period of time and removes them by oxidation;
The first flow for flowing the exhaust gas from one side of the filter and the second flow for flowing the exhaust gas from the other side of the filter can be switched alternately, and the exhaust gas bypasses the filter during the switching. Flowing exhaust switching means;
Unburned fuel supply means for supplying unburned fuel to the filter;
Simultaneous processing prohibiting means for prohibiting simultaneous execution of unburned fuel supply by the unburned fuel supplying means and exhaust gas flow switching operation by the exhaust gas switching means;
In the exhaust purification apparatus for an internal combustion engine Ru provided with,
The filter has a plurality of exhaust flow passages defined by partition walls formed of a porous material, and these exhaust flow passages are arranged upstream of each exhaust flow passage so that exhaust gas flowing into the filter passes through the partition walls. It is closed at the end or downstream end, and by switching the first flow and the second flow alternately by the exhaust gas switching means, the particulates in the exhaust gas are removed using both wall surfaces of the partition wall of the filter. An exhaust gas purification apparatus for an internal combustion engine, which collects and oxidizes and removes it. When the air-fuel ratio of the inflowing exhaust gas is lean, there is a NOx absorbent that absorbs NOx and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases, and an active oxygen release agent that promotes oxidation of fine particles A supported filter that can capture particulates in the exhaust gas for a period of time;
Exhaust air-fuel ratio control means for controlling the air-fuel ratio of the exhaust gas flowing through the filter to the theoretical air-fuel ratio or rich air-fuel ratio in order to release NOx from the NOx absorbent carried on the filter;
Exhaust gas switching means for normally flowing exhaust gas through the filter and flowing exhaust gas by bypassing the filter when the particulate oxidation performance in the filter is lower than or lower than a predetermined level;
When exhaust gas air-fuel ratio control is performed by the exhaust air-fuel ratio control means to release NOx from the NOx absorbent carried on the filter, the oxidation performance of fine particles in the filter is lower than the predetermined level. Detour prohibiting means for prohibiting the exhaust gas switching means from flowing the exhaust gas by bypassing the filter;
An exhaust emission control device for an internal combustion engine, comprising: A particulate filter for collecting particulates in the exhaust gas discharged from the combustion chamber is placed in the engine exhaust passage, and particulates in the exhaust gas are collected when the exhaust gas passes through the walls of the particulate filter. In the exhaust gas purifying apparatus for an internal combustion engine, the exhaust gas that can oxidize particulates temporarily collected by the particulate filter and passes through the wall of the particulate filter. Exhaust gas backflow means for reversing the flow of the exhaust gas is provided, and the exhaust gas backflow means has a bypass mode in which the exhaust gas can bypass the particulate filter without flowing into the particulate filter, and the exhaust gas When the first exhaust gas having a relatively small air-fuel ratio is flowing, the exhaust gas reverse The means is prohibited from being placed in the bypass mode, and when the second exhaust gas having a relatively large exhaust gas air-fuel ratio is flowing, the exhaust gas backflow means is allowed to be placed in the bypass mode. An exhaust purification device for an internal combustion engine. When the first exhaust gas having a relatively small exhaust gas air-fuel ratio is flowing, the flow of the exhaust gas that passes through the wall of the particulate filter in order to avoid the exhaust gas backflow means being placed in the bypass mode. When the second exhaust gas having a relatively large exhaust gas air-fuel ratio is flowing, the exhaust gas reverse flow means is accompanied by reversing the flow of the exhaust gas passing through the wall of the particulate filter. The exhaust emission control device for an internal combustion engine according to claim 3, wherein the exhaust gas is allowed to be disposed in a bypass mode. When it is necessary to reverse the flow of the exhaust gas passing through the wall of the particulate filter when the first exhaust gas having a relatively small exhaust gas air-fuel ratio is flowing, first, the particulate filter The exhaust gas air-fuel ratio is increased while prohibiting reversal of the flow of exhaust gas passing through the wall of the exhaust gas, and then reversal of the flow of exhaust gas passing through the wall of the particulate filter is allowed. An exhaust gas purification apparatus for an internal combustion engine as described. The first exhaust gas having a relatively small exhaust gas air-fuel ratio is stoichiometric or rich, and the second exhaust gas having a relatively large exhaust gas air-fuel ratio is lean. Exhaust gas purification device for internal combustion engine. A NOx absorbent that absorbs NOx in lean and releases NOx in stoichiometric or rich form is supported on the particulate filter, and when the NOx should be released from the NOx absorbent, the exhaust gas air-fuel ratio is made relatively small, and the NOx absorbent In order to prevent the exhaust gas backflow means from being placed in the bypass mode when NOx is released, reversal of the flow of exhaust gas passing through the wall of the particulate filter is prohibited. Item 6. An exhaust emission control device for an internal combustion engine according to Item 3. When the amount of inert gas supplied into the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas supplied to the combustion chamber is further increased Using an internal combustion engine in which the temperature of the fuel during combustion in the combustion chamber and the surrounding gas temperature is lower than the generation temperature of soot and soot is hardly generated, the fuel during combustion in the combustion chamber and the temperature of the gas around the combustion chamber When exhaust gas exhausted from the combustion chamber is flowing during low temperature combustion where the soot generation temperature is lower than the soot generation temperature and hardly generates soot, the exhaust gas backflow means is prohibited from being placed in the bypass mode. The exhaust emission control device for an internal combustion engine according to claim 3. During SOx poisoning recovery, NOx release, or engine low load operation, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is lower than the generation temperature of soot, and soot is almost generated. 9. The exhaust gas purification apparatus for an internal combustion engine according to claim 8, wherein when the exhaust gas discharged from the combustion chamber is flowing during low temperature combustion, the exhaust gas backflow means is prohibited from being placed in a bypass mode. . A particulate filter for collecting particulates in the exhaust gas discharged from the combustion chamber is placed in the engine exhaust passage, and particulates in the exhaust gas are collected when the exhaust gas passes through the walls of the particulate filter. In the exhaust gas purification apparatus for an internal combustion engine, the particulate filter can oxidize particulates temporarily collected by the particulate filter, absorbs NOx in lean, and is stoichiometric or rich in NOx. An exhaust gas backflow means for reversing the flow of exhaust gas that passes through the wall of the particulate filter is provided on the particulate filter, and the exhaust gas backflow means The particulate filter is bypassed without flowing into the particulate filter. When the exhaust gas backflow means should be placed in the bypass mode and NOx should be released from the NOx absorbent when the particulate oxidation performance by the particulate filter is lower than a predetermined level. The exhaust gas purification apparatus for an internal combustion engine, wherein the exhaust gas backflow means is prohibited from being placed in the bypass mode even when the particulate oxidation performance by the particulate filter is lower than the predetermined level.

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